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PROTEIN AND THE GLYCAEMIC INDEX
The Glycaemic Index was developed in 1981 by Dr. David Jenkins, a Professor
of nutrition at the University of Toronto as a tool to better understand how
the body responds to carbohydrates. It is essentially a ranking of a catalogue
of foods from 0 - 100 that tells us whether a food will raise blood sugar levels
dramatically, moderately, or a little.
Foods with a score of 60 or less are considered to have a low GI, whilst foods
with a score over 60 are considered to have a high GI.
Refined dietary sugars almost always turn into fats and starches can also turn
into saturated fats. This is the process by which carbohydrates enter the bloodstream
as sugar. This sugar is energy for your brain and body. If it is not used up
absolutely immediately it cannot just hang around in your blood stream doing
nothing. What does your body do? It secretes the storage hormone insulin in
response to your carbohydrate intake. This insulin then stores glucose in the
muscle and liver as stored glycogen, ready for immediately energy use. There
is a limit to how much glycogen that you can store within your muscle - obviously
limited by the size of your skeletal muscle tissue. Glycogen storage for a 150lb
athlete is radically different than a 300 lb Mr Olympia competitor - who definitely
can store much more. Of course once your muscle glycogen and liver are full
up to the maximum, the glucose must be converted into energy to be able to stored
for a later date. So what happens within the body is that your glucose is converted
into fat and the insulin itself, that was used as the hormone, is converted
into triglyceride and stored in your fat cells for use as energy of a later
date.
When you eat a carbohydrate rich meal your body responds by secreting the hormone
insulin form the pancreas. Insulin signals the fed-state and stimulates the
storage of fuels such as glucose. The greater the rise in blood-sugar, the more
insulin produced. Glucose is stored as Glycogen in the liver and the muscles.
This storage facility however has a limited capacity, any excess glucose that
cannot be stored as glycogen enters the adipose (fat) cells of the body and
stimulates the production of triacylglycerides. Consequently, if an individual's
blood-sugar constantly fluctuates above the maximum storage capacity the excess
glucose that they ingest will be stored as fat. Foods with a high GI factor
raise blood-sugar levels very high very rapidly and are therefore likely to
push glucose levels above that that can be stored by the body as glycogen. High
GI foods are therefore likely to promote the storage of fat. Foods with a low
GI factor raise blood-sugar levels slowly and steadily, just enough to keep
supplies of glycogen topped up without stimulating fat synthesis.
This is generally well known and accepted. Now, when you digest proteins, they
are themselves a different chemical structure than carbohydrates. Proteins are
not directly, nor initially, broken down into carbohydrate, although they can
be through another process. Proteins are digested and assimilated into their
amino acid components. This does not appear to raise blood glucose levels much
at all, and so you will probably not find many protein foods on the glycaemic
index rating or ranking. Although, this does not mean that protein does not
stimulate the release of insulin, because it does. Insulin is a storage hormone
and amino acids require storing. When you consume proteins with carbohydrate,
you generally have an overall lowering of the GI factor - a slightly slowed
release of sugar into the blood stream.
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